<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .outer{
            background:pink;
        }
        .inner{
            height: 400px;
            background-color: blue;
            margin-top:200px;
        }
    </style>
</head>
<body>
    <!-- 父元素的margin会和子元素重叠 -->
    <div class="outer">
        <div class="inner"></div>
    </div>
</body>
</html>